1. Field of the Invention
The present invention relates to a driving unit and a battery-assisted bicycle that assists a rider's pedaling effort with a driving force from an electric motor.
2. Description of the Related Art
There has been a known battery-assisted bicycle that detects a torque generated at a crankshaft rotated together with pedals by a torque detector and controls an electric motor based on a detection result in order to assist the rider's pedaling effort. In such a battery-assisted bicycle as disclosed in Japanese Patent No. 3108311, a fluctuation range of torque is detected and if the fluctuation range continues to be less than a prescribed range at least for a prescribed time period, an assist control is stopped.
In the structure disclosed in Japanese Patent No. 3108311, if the prescribed time period used as a criterion to stop the assist control is too short, the criterion is intermittently satisfied while the bicycle travels with a low crank rotation speed and the assist control can be suspended frequently. On the other hand, if the prescribed time period is too long, the time after a rider pushes on the pedals until the assist stops is prolonged.
As described above, if assistance is stopped based on the duration of a prescribed state as disclosed in Japanese Patent 3108311, the assist control may be suspended intermittently or the timing to stop the control considerably varies depending on the length of the prescribed time period used as the criterion to stop the assist control. Therefore, the structure may make a rider feel uncomfortable.